Population structure of Symbiodinium
sp. associated with the common sea fan, Gorgonia ventalina
, in the Florida Keys across distance, depth, and time

Abstract

Numerous marine invertebrates form endosymbiotic relationships with dinoflagellates in the genus Symbiodinium. However, few studies have examined the fine-scale population structure of these symbionts. Here, we describe the genetic structure of Symbiodinium type “B1/B184” inhabiting the gorgonian Gorgoniaventalina along the Florida Keys. Six polymorphic microsatellite loci were utilized to examine 16 populations along the Upper, Middle, and Lower Keys spanning a range of ~200 km. Multiple statistical tests detected significant differentiation in 54–92% of the 120 possible pairwise comparisons between localities, suggesting low levels of gene flow in these dinoflagellates. In general, populations clustered by geographic region and/or reefs in close proximity. Some of the sharpest population differentiation was detected between Symbiodinium from deep and shallow sites on the same reef. In spite of the high degree of population structure, alleles and genotypes were shared among localities, indicating some connectivity between Symbiodinium populations associated with G. ventalina.

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Supplementary Fig. 1. Ln likelihood estimates [P(X|K)] for the number of population clusters (k) in Symbiodinium of Gorgonia ventalina from the Florida Keys. Analysis includes all sampling locations (EPS 323 kb)

Supplementary Fig. 2. Delta K estimates for the number of population clusters (k) in Symbiodinium of Gorgonia ventalina from the Florida Keys. Analysis includes all sampling locations and was utilized to estimate the most likely number of population clusters as described in Evanno et al. (2005). (EPS 342 kb)

Supplementary Fig. 3. Ln likelihood estimates [P(X|K)] for the number of population clusters (k) in Symbiodinium of Gorgonia ventalina from the Florida Keys. Analysis includes only shallow sampling locations. (EPS 317 kb)

Supplementary Fig. 4. Delta K estimates for the number of population clusters (k) in Symbiodinium of Gorgonia ventalina from the Florida Keys. Analysis includes only shallow sampling locations and was utilized to estimate the most likely number of population clusters as described in Evanno et al. (2005). (EPS 344 kb)

Supplementary Fig. 5. Ln likelihood estimates [P(X|K)] for the number of population clusters (k) in Symbiodinium of Gorgonia ventalina from the Florida Keys. Analysis includes only deep sampling locations. (EPS 348 kb)

Supplementary Fig. 6. Delta K estimates for the number of population clusters (k) in Symbiodinium of Gorgonia ventalina from the Florida Keys. Analysis includes only deep sampling locations and was utilized to estimate the most likely number of population clusters as described in Evanno et al. (2005). (EPS 346 kb)

Supplementary Table 1. Allele frequencies within and across 16 Symbiodinium populations of Gorgonia ventalina in the Florida Keys for six microsatellite loci (dinucleotides: CA6.38, Gv2, Gv42; trinucleotides: Gv100, Sym155, Sym254). Most frequent allele is denoted in bold. The number of samples with single and multiple alleles are presented for each locus. n= the total number of alleles recovered at each sample location, “1 allele” is the number of samples containing a single allele, “2 alleles” is the number of samples containing 2 alleles, and “3 alleles” is the number of samples with 3 alleles at a given locus. Site abbreviations are given in Table 1. (DOC 301 kb)

Supplementary Table 2. Characteristics and distribution of the 388 genotypes identified from the Symbiodinium populations of Gorgonia ventalina in the Florida Keys. Genotypes are based on allele sizes (in bp) for six microsatellite loci. Genotype frequency by recovery location is denoted. Site abbreviations are given in Table 1 (DOC 559 kb)

Supplementary Table 3. Bayesian analyses of the Symbiodinium populations of Gorgonia ventalina in the Florida Keys. a) Proportion of individuals from each site assigned to the two proposed populations (clusters) using a Bayesian clustering method of the original 16 sample populations. Bold indicates the cluster that a majority of the samples from the original populations belong to (i.e., the most probable cluster). b) Proportion of individuals from shallow sites only assigned into four proposed populations. c) Proportion of individuals from deep sites only assigned into two proposed populations (DOC 71 kb)

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